Today, the United States imports vast amounts of petroleum to help satisfy its energy requirements. Volatile pricing, supply limitations, greenhouse gas emissions and the political and military costs associated with fossil fuels have all led to renewed interest in energy alternatives. But in addition to its use for fuel, many important basic chemical commodities are produced from oil. In fact, approximately 5% of the total output of a petroleum refinery is used by the chemical processing industry as raw materials (See Ragauskas, A. J. et al., The path forward for biofuels and biomaterials, Science 311:484-489 (2006), which is hereby incorporated by reference in its entirety) and as the cost of oil rises, so too does the cost of downstream commodity chemicals like plastic resins.
Fortunately, biomass can be a substitute feedstock for the production of fuel as well as many of the building block chemicals that are currently produced from oil. Because petroleum and biomass are both carbon-based, chemicals (including relatively linear polymers and polymer building blocks) that are based on non-renewable petroleum products can also be produced from renewable biomass using current fermentation techniques.
Unfortunately, the use of agricultural crops as a source of biomass for chemicals and energy suffers from at least two disadvantages. First, raising crops is oil intensive. Farm equipment needs fuel to weed, till and harvest. Moreover, fertilizers and pesticides are often produced from petroleum. Second, crops and land are needed to feed both humans and domestic animals, and their use to produce an industrial feedstock escalates competition between the use of land for food or for fuel. The United Nations Food & Agricultural Organization (FAO) reports that the average price of corn increased 85% between the years of 2000 and 2007 as a direct result of rising farm energy costs and increased demand from ethanol and bioplastics producers. In fact, in 2007 about 25% of the US corn crop was diverted into ethanol production and the rate is accelerating. See ICIS Chemical Business, Biofuels backlash grows in fuel versus food debate, Simon Robinson, London, Feb. 11, 2008, which is hereby incorporated by reference in its entirety.
A better alternative to the use of agricultural biomass is selective tree cutting, which is sustainable and requires little cultivation. Due to vertical tree growth, it produces a much greater yield of biomass per acre. In a recent report, the Pacific Northwest National Laboratory (PNNL) and the National Renewable Energy Laboratory (NREL) summarized the results of an extensive screening study of the possibilities for processing the sugars derived from woody biomass into basic chemicals. See Werpy, T. and Peterson, G., Top value added chemicals from biomass, Volume I, Results of screening for potential candidates from sugars and synthesis gas, produced for the NREL, Publication No. DOE/GO-102004-1992, August 2004, which is hereby incorporated by reference in its entirety. Among the 300 possible products listed were the top 30 building block chemicals of industry. Of particular interest are itaconic acid and lactic acid, the bifunctional organic acids derived from fermentation that can be made into a wide variety of plastic products.
North American forests contain huge amounts of woody biomass and the cost per ton of raw material is significantly less than for agricultural biomass. However, the drawback to using wood for chemical production and biofuels has been, and continues to be, the difficulty and inefficiency of fractionating wood into its three basic components, namely, cellulose, hemicellulose and lignin. Effective separation would allow the hemicellulose (a branched and relatively short chain of simple sugars) to be utilized for fermentation into chemical products, instead of being burned as waste. It is estimated that 60-80% of the cost of manufacturing chemical products from agricultural biomass is incurred in separating fermentable sugars from the starting material. See Ragauskas, A. J. et al., 2006, supra. For forest biomass, with complex linkages between its three components, this percentage is likely larger. Therefore, decreasing the cost and increasing the efficiency of separation will have a substantial effect on the economic feasibility of using forest biomass for chemical and biofuel production.
The first step toward cost-effective use of forest biomass has been the conceptualization of the integrated forest biorefinery (IFBR) co-located with pulp and paper mills. In such a system, value is maximized by diverting high-value cellulose to papermaking, in effect subsidizing the separation cost. The lignin and hemicellulose can then be made available for further processing instead of being burned for energy, as is currently the case. At present, IFBRs are targeting hardwood as a raw material. This is because softwoods are more extensively cross-linked, making it harder to extract their hemicellulose. However, the predominant softwood hemicellulose (mannan) is made of more easily fermentable sugars. A cost-effective method of extracting mannan and xylan from softwoods and hardwoods would yield superior hemicellulose feedstreams.
Therefore, there is a need to develop innovative, efficient, cost-effective and non-damaging procedures for fractionating woody biomass (e.g. hardwoods and softwoods) for chemical and fuel production. There is also a need to develop methods for separating woody biomass into hemicellulose, cellulose and lignin components that are clean and gentle and at conditions that maintain the functionality and downstream use of each of these components. This invention answers those needs.